The study reported in the British Medical Journal shows that the blood sample collected from both the pregnant mother and the fetus can be used to analyse the genetic material in the blood through a process called multiplexed maternal plasma DNA sequencing.
Till now the genetic disease has been detected through tests like amniocentesis and CVS (chorionic villus sampling). These are carried usually in the 10th to 15th week period of pregnancy and are also used to detect other birth defects. They are done by taking a tiny sample of the amniotic fluid surrounding the placenta. While the tests are reliable, they have a 0.5 to 1.0 percent chance of leading to miscarriage.
They are also not 100 percent accurate sometimes giving false negatives. This means that a Down’s syndrome case may go undetected as the result comes negative. There have also been cases of false positives.
The new blood test was studies and researched by a team of experts led by Prof. Dennis Lo of The Chinese University of Hong Kong. In the study, 753 pregnant women in Hong Kong, the U.K. and the Netherlands who had chances of having babies with down’s syndrome were given the test. Of these 86 were found to be carrying the baby with the syndrome. What was a more valuable find was that none of the results were false negatives.
The researchers therefore feel that the blood test can be definitely used to rule out Down’s syndrome in high risk pregnancy cases before the invasive tests are used.
Some doctors, however, feel that there are more hurdles to cross before the test can be used commonly. Dr. Mark I. Evans, an obstetrician at Mount Sinai School of Medicine in New York City feels that during high risk pregnancy there are other birth defects too that need to be found out and not just down syndrome. He says,
“The bad news is that prenatal diagnosis is not just about Down syndrome. Down syndrome represents about 50 per cent of what we find, and this new test can help with that. But it may also give women a false sense of reassurance.”
The test is also quite expensive presently. An early screening test costs $100 while a commercial version being developed may cost $ 700. – Atula, Staff Writer
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